Normally, separation of large molecules (including, for example, DNA) by size in chromatography or in electrophoresis requires use of another large polymer molecule. The most widely used method for separating such large molecules in an electrophoresis system is the use of a gel-sieving matrix.
In recent years, many new gel materials have been described in the scientific literature or disclosed in patents. These materials include polymers made by chemically linking various monomers, or by linking combinations of monomers and cross-linkers, or modified natural polymers.
Non-ionic polymeric surfactants have been used successfully as a separation medium for DNA analysis. These block copolymers have a hydrophobic core of propylene oxide blocks and a strongly hydrated shell of ethylene oxide blocks that can form micelles in solution. The aggregation number is determined by the length of the propylene oxide block. With increasing temperature desolvation of the ethylene oxide groups continues, and the effective volume fraction decreases. These globular micelles overlap and entangle each other at high concentrations. Ultimately, lyotropic liquid crystals are formed that are used as the sieving medium. The spherical micelles that result rely on partitioning based on micellar electrokinetic chromatography or adsorption of the monomers along the DNA chains.
However, these polymers are not always stable due to degradation with time, the testing environment and mechanical shearing during preparation. The separation performance can thus deteriorate due to such degradation.
In addition to degradation over time, the polymeric sieving mediums most commonly employed are relatively difficult to use. Accordingly, for example, filling the capillary tubes used for electrophoresis, and then cleaning such tubes after use, can be, and generally is, relatively difficult. Often, it becomes necessary to replace the capillary tubes due to contamination (stemming from retained sieving medium and/or sample solution).
Also, a polymeric sieving medium cannot be altered. More particularly, the molecular weight of the polymer fixes the application. There is no ability to alter the polymer sieve medium to tailor the medium to different samples having analytes that would optimally require a polymer of a different molecular weight to serve as the sieve medium, i.e., different polymer sieve mediums often will be required for different samples due to the differing composition of the samples.
It would accordingly be highly desirable if it were possible to effect size separation of large molecules using a sieve medium that possessed a relatively low viscosity prior to, and after, size separation so that the sieve medium could be readily put into place, and then easily removed after use. Even further, it would be highly advantageous if a sieving medium could be provided that could be readily tailored to the requirements of a particle sample, so as to allow an efficacious and optimal size separation of the target analyte(s) in such sample.